1. Field of the Invention
The present invention relates generally to a battery management system, and more particularly, to a method and apparatus for detecting voltage of a battery cell in consideration of impedance of conductive wires connecting a plurality of battery cells constituting the battery pack.
2. Description of the Prior Art
In general, voltage and current of a battery cell are separately detected in a battery management system. Lasting efforts are made to improve the precision of detecting the voltage and current of the battery cell.
Especially, technology of detecting the current of the battery cell is improved in precision by introducing an algorithm into the hardware, while technology of detecting the voltage of the battery cell is limited only to development of hardware technology.
In the battery management system, the most important factor is to calculate a state of charge (SOC) of the battery by means of accurate detection of the current. The SOC is compensated in the proximity of discharge end voltage. Because a time for this compensation is determined by reference voltage, the accurate voltage detection of the battery cell is essential to calculate the SOC of the battery.
A configuration of the conventional battery management system will be described with reference to FIG. 1.
Referring to FIG. 1, the conventional battery management system comprises a battery pack connecting a plurality of battery cells C1, C2 and C3 in series or in parallel, a voltage detector 101 detecting the voltage of the battery cells C1, C2 and C3 constituting the battery pack, a resistor 102 detecting charge/discharge current flowing through the battery pack, a current detector 103 detecting current across the resistor 102, a controller 104 summing up and controlling the voltage and current detected through the voltage and current detectors 101 and 103, and a communication unit 105 taking charge of communication between the controller 104 and external equipment. The voltage detector 101, the current detector 103, the controller 103, and the communication unit 105 are included in a fuel gauging integrated circuit (IC) formed into one chip.
The battery pack connected in series by the plurality of battery cells has a cathode (+) connected with a plus terminal B+of power output terminals, and an anode (−) connected with a minus terminal B−. Further, the cathode (+) and anode (−) of the battery pack and two contacts between the plurality of battery cells C1, C2 and C3 constituting the battery pack are connected to the voltage detector 101.
The voltage detector 101 is connected to each of the contacts between the plurality of battery cells C1, C2 and C3 connected in series, and detects voltage between the respective contacts without considering impedance of conductive wires connecting the battery cells. Hence, the voltage measured by the voltage detector 101 includes an error corresponding to a drop/rise value of voltage caused by the impedance of the conductive wires.
In this manner, conventionally, the voltage is detected without taking into consideration the impedance of the conductive wires connecting the battery cells, so that there is no alternative but to include the error caused by the impedance of the conductive wires.
This error lowers precision of calculating the actual SOC of the battery, which is responsible for short duration of the battery pack or abnormal protection.
Further, the error increases as the current flowing in the battery pack becomes higher.